1. Technical Field
Embodiments described herein relate to an inverter device including a switch circuit configured by series-connecting two N-channel semiconductor switching elements in opposite directions so that the switch circuit makes or breaks electrical connection between a DC power supply and an inverter circuit, and a power steering device provided with the inverter device.
2. Related Art
An electrically driven power steering device includes a steering torque sensor detecting input steering torque supplied via a handle manipulated by a driver and a control device determining the magnitude and direction of motor output based on an output signal of the steering torque sensor. An electric motor is driven via an inverter circuit, so that power of the motor is transmitted to a steering system thereby to reduce the steering torque.
In conventional electrically driven power steering devices, a switch configured by a relay is inserted between a battery as a power supply and the inverter circuit. When detecting an overcurrent state or malfunction of PWM control, the control device opens the switch to cut off electrical power supply to the inverter circuit and the motor, thereby preventing the motor from producing an undesired assist steering force. However, the switch configured by the relay is required to supply a large current of about several tens of amperes to 100 amperes to the motor in order that the assist steering torque may be generated. A relay which can interrupt such a large current as mentioned above is large in size, resulting in a large-sized power steering device. In view of the circumstances, a switch circuit using a semiconductor switching element such as FET instead of the relay has been proposed.